Are C Struct Members Automatically Zero-Initialized?

Value Initialization of Struct Members in C

Consider the following struct:

struct Snapshot
{
    double x; 
    int y;
};

If the struct is declared without initialization, are its members automatically set to 0?

Answer:

No, members are not automatically initialized to 0. To set them to 0, explicit initialization is required:

Snapshot s = {0,0};

Other Initialization Options:

• Value Initialization ({}): Initializes all members to their default values, e.g., 0 for numeric types.

Snapshot s = {}; // All members set to 0

• Default Constructor: If the struct has a default constructor with member initialization, it will be used for implicit initialization.

struct Snapshot {
    int x = 0;
    double y = 0.0;
};

Snapshot s; // x = 0, y = 0.0

• Constructor with Member Initialization: Custom initialization can be done using constructors.

struct Snapshot {
    Snapshot(int x, double y) : x(x), y(y) { }
};

Snapshot s(0, 0.0); // x = 0, y = 0.0

Note: Constructor initialization is not possible if there are aggregate initializer lists present in the struct declaration.

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